Method for the production of a synthetic leather

ABSTRACT

A synthetic leather made of a nonwoven fabric impregnated and/or coated with a polymer, with a surface weight of 100 to 500 g/m 2 , and a tensile strength greater than 300 N/5 cm in the lengthwise and the crosswise direction, where the nonwoven fabric is made up of melt-spun multi-component endless filaments, aerodynamically stretched and directly laid up to form a nonwoven material, having a titer less than 2 dTex, and wherein the multi-component endless filaments, after preliminary bonding, are split and bonded by at least 90% to produce supermicro endless filaments having a titer less than 0.2 dTex.

The invention relates to a synthetic leather made of a nonwoven fabricimpregnated and/or coated with a polymer, with a surface weight of 100to 500 g/m², and a tensile strength >300 N/5 cm in the lengthwise andthe crosswise direction.

From the document European Patent Application 0 090 397, nonwovenfabrics made of ultrafine, tangled filaments are known, which have alayer structure and can be processed to produce synthetic leather, byimpregnating and/or coating them with polymers. Preferably, fibers ofthe “island-in-sea” type are used as the starting fibers, where theultrafine fibers are released by dissolving the matrix polymer.Furthermore, the use of splittable starting fibers is also indicated.

The document European Patent Application 0 624 676 discloses nonwovenfabrics made of ultrafine fibers and processes for their production frombicomponent fibers. In this connection, the starting polymers of thebicomponent fibers are supposed to have a difference in melting point of30 to 180° C., and are spun as multi-segment fibers. The bicomponentfibers, which are deposited to form a fiber layer, are subjected topoint calandering, during which only the fiber component with the lowermelting point is partially melted and consolidated. In a subsequentstep, the nonwoven fabric formed from the multi-segment fibers is split,by at least 70%, into the ultrafine partial segment fibers by mechanicalaction on the fibers. The nonwoven fabrics obtained in this way achievetensile strength values in the lengthwise and crosswise direction of amaximum of 260 N/5 cm, and can be used as bed linens, absorbents forsanitary products, such as tissues, diapers, filling for sleeping bags,artificial leather, thermal insulation materials, and other purposes.

The invention has set itself the task of indicating inexpensivesynthetic leathers with a high tensile strength, as well as a processfor their production.

This task is accomplished, according to the present invention, by asynthetic leather that is made of a nonwoven fabric impregnated and/orcoated with a polymer, with a surface weight of 100 to 500 g/m², as wellas a tensile strength >300 N/5 cm in the lengthwise and the crosswisedirection, where the nonwoven fabric is made up of melt-spun,aerodynamically stretched multi-component endless filaments, with atiter <2 dtex, immediately deposited to form a nonwoven layer, and themulti-component endless filaments, after preliminary bonding, are splitby at least 90% to produce supermicro endless filaments with a titer<0.2 dtex, and bonded. Such a synthetic leather demonstrates hightensile strength at a relatively low weight, and is thereforeinexpensive. Furthermore, it is similar to natural materials in terms ofits feel.

Preferably, the synthetic leather is one in which the multi-componentendless filament is a bicomponent endless filament of two incompatiblepolymers, particularly a polyester and a polyamide. Such a bicomponentendless filament demonstrates, good splittability into supermicroendless filaments and results in an advantageous ratio of strength tosurface weight.

Preferably, the synthetic leather is one in which the multi-componentendless filaments have a cross-section with an orange-like multi-segmentstructure, where the segments alternately contain one of the twoincompatible polymers. In addition to this orange-like multi-segmentstructure of the multi-component endless filaments, other arrangementsof the incompatible polymers in the multi-component endless filament arealso possible, such as a side-by-side arrangement or an arrangementsimilar to chrysanthemum petals. Such arrangements of the incompatiblepolymers in the multi-component endless filament have proven to be verywell capable of being split.

Preferably, the synthetic leather is furthermore one in which at leastone of the incompatible polymers that forms the multi-component endlessfilament contains an additive, such as dyeing pigments, permanentlyacting anti-statics and/or additives that influence the hydrophilic orhydrophobic properties, in amounts up to 10 percent by weight. Thesynthetic leather made up of spin-dyed fibers has a very high resistanceto fading at high temperatures. Furthermore, the additives can be usedto reduce or prevent static charges, and to improve moisture transportproperties.

A synthetic leather in which the nonwoven fabric is impregnated with 10to 45 percent by weight of a polymer, with reference to the startingweight of the nonwoven fabric, is particularly preferred. For the sameor actually superior strength properties of the synthetic leather, alesser degree of impregnation is required, according to the invention,as compared with previously known products.

The process according to the present invention, for the production of asynthetic leather, includes the steps that multi-component endlessfilaments are spun from the melt, aerodynamically stretched, andimmediately deposited to form a nonwoven layer, that preliminary bondingtakes place, and that the nonwoven fabric is bonded by high-pressurefluid jets and, at the same time, split into supermicro endlessfilaments with a titer <0.2 dtex, and subsequently impregnated and/orcoated with a polymer. The synthetic leathers obtained in this way arevery uniform with regard to their thickness, they demonstrate anisotropic filament distribution, do not possess any tendency towardsdelamination, and are characterized by high modulus values.

It is advantageous if the method for the production of the syntheticleather is carried out in such a manner that bonding and splitting ofthe multi-component endless filaments takes place in that the pre-bondednonwoven fabric is alternately impacted from both sides withhigh-pressure water jets, several times. As a result, the startingnonwoven fabric for the synthetic leather demonstrates a good surfaceand a degree of splitting of the multi-component endless filaments >90%.

It is advantageous if the process for bonding and splitting of themulti-component endless filament is carried out on a unit with rotatingscreen drums. Such a unit permits the construction of very compactsystems.

It is advantageous if the nonwoven fabric, bonded with high-pressurefluid jets and split into supermicro endless fibers, is impregnated witha polyurethane dissolved in dimethyl formamide, and if the polymercoagulates in known manner.

It is especially preferred in the production of the synthetic leatheraccording to the present invention that impregnation of the nonwovenfabric is carried out using an aqueous polyurethane latex dispersion,and coagulation takes place subsequently. This form of impregnation ofthe starting nonwoven fabric results in no residues of solvent, and istherefore environmentally friendly.

A method in which the multi-component endless fibers are spin-dyed isparticularly preferred. Binding the dye into the polymer fibers resultsin excellent resistance to fading at hot temperatures.

It is furthermore preferred, for various applications, that subsequenttreatment by polishing or buffing takes place. In this way, the feel andthe surface properties can be improved, and in addition, a so-called“writing effect” can be achieved. “Writing effect” is understood to meanexposure of the microfiber ends at the surface of the synthetic leather,which ends can be oriented in visible manner.

The synthetic leathers produced according to the present invention areparticularly well suited for use in the shoe industry, as a material forshoe uppers, interior linings, trim, or heel linings. They arefurthermore suitable as clothing materials. Because of their goodmechanical strength and, in the case of spin-dyed products, because oftheir great resistance to fading at high temperatures, the syntheticleathers according to the invention are suited for use in automobileinteriors, for the production of dashboards, side paneling, rear windowshelves, interior roof coverings, or trunk paneling, and for theproduction of upholstered furniture, particularly as upholsterymaterials for armchairs, sofas, or chairs.

EXAMPLE 1

A filament pile with a surface weight of 160 g/m² is produced from apolyester-polyamide (PES-PA) bicomponent endless filament and subjectedto water-jet needle-punching at pressures up to 250 bar on both sides.After the water-jet needle-punching, which results in simultaneoussplitting of the starting filaments, the bicomponent endless filamentshave a titer <0.2 dtex. The bonded nonwoven fabric is subjected toimpregnation with a polyurethane (PUR) dissolved in dimethyl formamide(DMF), where approximately 12 wt.-% PUR are applied, with reference tothe starting weight of the nonwoven fabric. The polymer-impregnatednonwoven fabric obtained in this way is surface-ground and finished withspecial silicones, for example, in order to improve the feel. Asynthetic leather with a nubuck-like surface is obtained.

EXAMPLE 2

A filament pile with a surface weight of 110 g/m² is produced from aPES-PA bicomponent endless filament and subjected to water-jetneedle-punching at pressures up to 250 bar on both sides. After thewater-jet needle-punching, which results in simultaneous splitting ofthe starting filaments, the bicomponent endless filaments have a titer<0.2 dtex. The bonded nonwoven fabric is subjected to impregnation withan aqueous polyurethane latex dispersion, where approximately 10 wt.-%PUR are applied, with reference to the starting weight of the nonwovenfabric. The polyurethane is coagulated by treatment with hot water orsaturated steam, and subsequently dried and crosslinked at approximately150 to 160° C. The polymer-impregnated nonwoven fabric obtained in thisway is surface-ground and finished with special silicones, for example,in order to improve the feel. A synthetic leather with a nubuck-likesurface is obtained.

1. A method for the production of a synthetic leather, the methodcomprising the steps of: spinning multi-component endless filaments froma melt; aerodynamically stretching the multi-component endlessfilaments; directly depositing the multi-component endless filaments toform a nonwoven material; performing a preliminary bonding step; bondingthe nonwoven fabric by high-pressure fluid jets; splitting the nonwovenfabric into supermicro filaments having a titer less than 0.2 dTex; andat least one of impregnating and coating the nonwoven fabric with apolymer.
 2. The method according to claim 1, wherein the steps ofbonding and splitting the multi-component endless filaments includes thesteps of alternately impacting the multi-component endless filamentsfrom both sides with high-pressure fluid jets, several times.
 3. Themethod according to claim 2, wherein the steps of bonding and splittingthe multi-component endless filament is performed on a unit withrotating screen drums.
 4. The method according to claim 1, wherein thestep of impregnating the nonwoven fabric is performed using a polymerwith a polyurethane dissolved in dimethyl formamide, and wherein thepolymer is coagulated.
 5. The method according to claim 1, wherein thestep of impregnating the nonwoven fabric is performed using a polymerwith an aqueous polyurethane latex dispersion.
 6. The method accordingto claim 1, further comprising the step of dyeing the multi-componentendless filaments by spin-dyeing.
 7. The method according to claim 1,further comprising at least one of the steps of polishing and buffing.8. The method according to claim 2, further comprising the step of usingthe synthetic leather as a material for at least one of shoe uppers,interior linings, trim, and heel linings in a shoe.
 9. The methodaccording to claim 2, further comprising the step of using the syntheticleather for the production of at least one of dashboards, side paneling,rear window shelves, interior roof coverings, and trunk paneling in anautomobile interior.
 10. The method according to claim 2, furthercomprising the step using the synthetic leather in at least one ofclothing or as upholstery material for at least one of the armchairs,sofas, and chairs.
 11. The method according to claim 1, wherein theimpregnating the nonwoven fabric with a polymer occurs with 10 to 45percent by weight of the polymer, with reference to the starting weightof the nonwoven fabric.